1. Field of the Invention
This invention relates to an audio signal transmitting apparatus and the method thereof, and more particularly to an improvement of an audio signal transmitting apparatus which is applicable to a recording and/or reproducing apparatus for recording and/or reproducing an audio signal on a recording medium.
2. Background of the Invention
A digital audio tape recorder generally converts an audio signal into a digital signal and records the signal on a magnetic tape to record and/or reproduce the audio signal with high tone quality.
This digital audio tape recorder samples audio signals input sequentially at a sampling frequency of 48 [kHz] or 44.1 [kHz], and performs analog-to-digital conversion to convert the audio signal into a 16-bit per sample digital signal.
A frequency of 20 [Hz] to 20 [kHz] is known to be the human audio frequency band in general. Accordingly, the digital audio tape recorder selects any of the above sampling frequencies so that the audio signal can be converted into a digital signal at a frequency band almost equal to the human audio frequency band.
The digital audio tape recorder divides the digital signal into specified blocks, adds an error correction code to each block, and interleaves the signal to generate record data.
The tape recorder uses this record data to drive a magnetic head to sequentially record the record data on a magnetic tape.
After converting, reproducing signal output from the magnetic head into binary data, the digital audio tape recorder performs a procedure which is the reverse of that performed in recording, so as to demodulate the original audio signal. Thereby, in the digital audio tape recorder, the deterioration of the tone quality can be effectively avoided in recording and reproducing.
In this type of digital audio tape recorder, a digital audio tape recorder (hereinafter referred to as "double-speed recording and reproducing digital audio tape recorder") has been proposed in which the rotating speed of a rotary drum is set to a value double the normal speed, and also the running speed of a magnetic tape is set to a value double the normal speed, so that an audio signal with a higher tone quality can be recorded and/or reproduced.
In this double-speed recording and/or reproducing digital audio tape recorder, the sampling frequency can be set to a value double the normal sampling frequency of the digital audio tape recorder, thus the recordable and reproducible frequency band can be increased to twice the width of the normal digital audio tape recorder.
Therefore, the double-speed recording and/or reproducing digital audio tape recorder can set the cutoff frequency of an antialiasing filter used to limit the band to a sufficiently higher frequency than the human audio frequency band, thereby, the deterioration of the transient characteristic within the audio frequency band can be substantially reduced compared with the normal digital audio tape recorder.
However, since the number of recordable and reproducible requantizing bits of the double-speed recording and/or reproducing digital audio tape recorder is the same as that of the normal digital audio tape recorder, the former tape recorder improves the frequency characteristic but fails to improve the amplitude characteristic compared to prior art.
If the characteristic of the double-speed recording and/or reproducing digital audio tape recorder can be used effectively and the amplitude characteristic can be improved easily, the tone quality and usability of the digital audio tape recorder may be further improved.
In the digital audio tape recorder which performs recording and/or reproducing at double-speed, a reproduced-data transfer rate is double that of the normal digital audio tape recorder, thus the time required for transfer is doubled if a digital audio interface compatible with digital audio signal is used to transfer reproduced data.
As a further disadvantage, reproduced audio data cannot be transmitted in real time even if the frequency characteristic is improved and the amplitude characteristic enhanced.